The overall goal of our research program is to understand the function and ontogeny of nonhuman primate vocal communication in complex social contexts. The long-term aim of this work is to explore cognitive dimensions of primate behavior that may ultimately provide insights into the evolutionary origins of human language. A recent focus has been the evolution of skeptical responding in primates as a response to deception. While deceptive signalers may become devalued as sources of information, 'skepticism' and any efforts involved in testing reliability entail costs that involve delays and energy expenditures. Skepticism may be less costly though, if, as a rule, animals are not equally skeptical of the signals of all conspecifics. Animals with the ability to recognize individual conspecifics and recall past encounters with them may have the capacity to restrict skepticism to those subsets of animals most likely to benefit from deception. Tape-recorded alarm calls of high-and low-ranking rhesus monkeys were played to their groups in a feeding context once daily until habituation occurred. Response was greater to the calls of high-ranking monkeys, adult response patterns were different from those of juveniles and, for adults especially, decline in responsiveness was punctuated by partial resurgence of response. These differences may be the consequence of the adults' more extensive history of interaction with group members that, though generally reliable, vary with respect to the potential benefits of deceptive signaling.
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